MW vs. MWh
Unlike conventional generation, which is typically measured only in megawatts, energy storage systems have both power and energy ratings. It is vital to understand the difference between these units of measurement.
- Power is measured in kilowatts (kW) or megawatts (MW) and refers to the amount of electricity a storage system can absorb or supply at any given instant.
- Energy is measured in kilowatt-hours (kWh) or megawatt-hours (MWh) and refers to the total storage capacity of a system, or the length of time a battery can provide a set amount of power.
This relationship between power and energy can be illustrated by the example of a water tank with pipes used to fill up or empty the tank. As you might expect, the rate at which water flows from the tank is determined by the diameter of the pipe attached to tank. The rate at which water flows through the pipe is analogous to a storage system’s electrical POWER (MW) capacity. Similarly, the length of time the pipe will dispense water is limited by the amount of water the tank can hold. The capacity of the tank is analogous to a storage system’s electrical ENERGY (MWh). It is extremely beneficial for an energy storage system to be able to size its power and its energy separately to optimize its benefit on a project-by-project basis.